In 1874, kidnapping was a misdemeanor under Pennsylvania law. Then 4-year-old Charley Ross went missing. Two men had picked him and his 5-year-old brother up, but the older boy was set free the same day. Christian Ross, the boy's father, went to police, who didn't take the case seriously -until the first ransom note showed up.

Somebody had written the message—ridden with errors in spelling, capitalization and punctuation—in black ink and an unsteady hand. “You wil have to pay us before you git him from us, and pay us a big cent to,” the note read. “if you put the cops hunting for him you is only defeeting yu own end.”

The second came five days later, stating the ransom amount: “This is the lever that moved the rock that hides him from yu $20,000. Not one doler les—impossible—impossible—you cannot get him without it.” (The sum of $20,000 in 1874 was the equivalent of about $400,000 today.)

With this demand, the letter writers recorded the first ransom kidnapping in U.S. history. They told Christian Ross to correspond with them through the personal advertisements of the Philadelphia Public Ledger.

The police then went into full investigation mode, asking the public for tips and eventually offering a huge reward. Newspapers covered the case and parents panicked. One lead led to the police hiring a spy to investigate suspects. Two suspects died during another crime and one was arrested, but the case was never truly solved. However, Pennsylvania made kidnapping into a felony crime.

Fast forward 139 years, when a librarian in Philadelphia uncovered a set of 22 letters among her family's possessions. They had found the original ransom notes, which were thought lost forever. But how did they come into her family's possession? Read the story of the kidnapping and those ransom letters at Smithsonian's Past Imperfect blog.